Sent email message move to your Outbox folder but never move to your Sent Items folder.
After you send a message, Outlook moves the message to your Outbox. When Outlook establishes a connection to your email server, the application tries to deliver the message, and a copy of the message appears in your Outbox. If you open and close a message while it is still in your Outbox, you change the status of the message, and it is not sent.
Step 1: Make sure Outlook is not offline
Outlook 2011 might be set to Work Offline. Check to see whether Outlook is offline. To do this, follow these steps:
Click the Outlook menu, and see whether the Work Offline option has a check mark. If there is a check mark, click Work Offline again.
Step 2: Empty the Outlook send folder
Open the Send folder in Outlook, and then delete all messages that are listed there. Quit Outlook. Restart Outlook, and then try sending or receiving email.
Step 3: Use the Shift key and restart Outlook
Quit Outlook if it is running. Press and hold the Shift key on your keyboard as you restart Outlook.
If the issue continues to occur, rebuild the Outlook database. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2360509 Rebuild the identity database to resolve problems in Outlook for Mac 2011